Implementation of Wiener Algorithm for Spectral Reflectance Reconstruction of 3 and 6 Channel Images

Wiener estimation is a widely used technique for the spectral reflectance reconstruction of colored objects. In our study the reflectance estimation of 3-channel images acquired using traditional RGB camera was compared with that of 6-channel images captured by a modified 6-channel camera. 240 patches of ColorChecker DC Chart were used for training and testing of the models.Their performance was assessed via quality metrics PSNR, RMSE and CIE DE2000 based on the reconstructed and spectrophotometrically measured reflectance values. Compared to the 3-channel models, 6-channel models in general provided better results. Lowest color difference CIE DE2000 was obtained when using 10 calculation terms in the 3-channel algorithm and 13 terms in the 6-channel. Best reconstruction models, i.e. lowest CIE DE2000 and RMSE and highest PSNR values, were found for the skin and neutral tones while the performance was the poorest with the saturated color patches. The obtained results can be of use in various practical applications, such as in a printing workflow with high precision color rendering or for accurate digitization of paintings and other works of art

Influence of a multichannel image acquisition on the reflectance estimation

Uporaba Wienerjevega filtra je široko uporabljana tehnika za rekonstrukcijo stopnje refleksije (spektralnih reflektanc). V disertaciji smo oceno stopnje refleksije 3-kanalnih slik, pridobljenih s tradicionalno RGB-kamero, primerjali z oceno stopnje refleksije 6-kanalnih slik, posnetih z modificirano kamero. Za učenje in testiranje modelov je bilo uporabljenih 240 polj barvne tablice ColorCheckerDC. Učinkovitost modelov je bila vrednotena z metrikami PSNR, RMSE in CIEDE2000 na podlagi rekonstruiranih in spektrofotometrično izmerjenih polj stopnje refleksije. V primerjavi s 3-kanalnimi so 6-kanalni modeli na splošno dali boljše rezultate. Najmanjša barvna razlika – CIEDE2000 – je bila dosežena z uporabo desetih členov pri 3-kanalnem in trinajstih členov pri 6-kanalnem algoritmu. Najboljši modeli, tj. najnižje vrednosti CIEDE2000 in RMSE ter najvišje vrednosti PSNR, so bili ugotovljeni za kožne in nevtralne tone, medtem ko je bila učinkovitost najslabša pri nasičenih poljih. Dobljeni rezultati so uporabni v različnih praktičnih aplikacijah, na primer v delovnem procesu tiskanja z visoko natančnostjo barvnega upodabljanja ali za natančno digitalizacijo slik in drugih umetnin. Zaradi zahtevnosti posameznih področij v večkanalnem delokrogu (od zajema do tiska) smo opustili misel, da bi v disertaciji obdelali celoten spektralni delokrog, in smo se osredinili le na 3- in 6-kanalni zajem. Tako smo tekom disertacije v Darmstadtu z modificirano kamero uspešno zajeli poleg testnih tablic tudi umetniška dela in jih tako zelo kakovostno digitalizirali oziroma shranili za nadaljnjo uporabo v format, ki ima še veliko rezerv in potenciala ter z uporabo različnih algoritmov omogoča zanimive raziskave in nadaljnje analize v prihodnosti. V drugem sklopu disertacije nas je zanimala kolorimetrična natančnost zajema konvencionalnih digitalnih kamer, ki je bila prikazana na podlagi metrike CIEDE2000 in izdelave profilov kamer ICC ter z vidika izračunov volumnov profilov kamer. Na podlagi primerjave povprečnih barvnih razlik CIEDE2000 med kamerami in volumni profilov smo razbrali trend, ki nakazuje, da kamere z večjimi volumni profilov (barvnimi obsegi) zagotavljajo nižje vrednosti barvnih razlik in nasprotno.Wiener estimation is a widely used technique for the spectral reflectance reconstruction of colored objects. In our study, the reflectance estimation of 3-channel images acquired using a traditional RGB camera was compared with that of 6-channel images captured with a modified 6-channel camera. 240 patches of ColorChecker DC Chart were used for training and testing of the models. Their performance was assessed via the quality metrics PSNR, RMSE and CIEDE2000 based on the reconstructed and spectrophotometrically measured reflectance values. Compared to 3-channel models, 6-channel models in general provided better results. The lowest color difference – CIEDE2000 – was obtained when using 10 calculation terms in the 3-channel algorithm and 13 terms in the 6-channel. The best reconstruction models, i.e. the lowest CIEDE2000 and RMSE, and the highest PSNR values, were found for the skin and neutral tones while the performance was the poorest with the saturated color patches. The obtained results can be of use in various practical applications, e.g. in a printing workflow with high precision color rendering or for accurate digitization of paintings and other artworks. Due to the complexity of individual steps within the multi-channel workflow (from capture to print) and understanding of the challenges and specificities of each step, the dissertation focused solely on the capture process. Consequently, during the research work which took place in Darmstadt, we successfully captured not only test charts but also artworks using the modified camera, thereby effectively digitizing and preserving them for further use. This format still holds a significant potential and provides a basis for engaging research and further analysis using various algorithms in the future. In the second part of the research, we also focused on the colorimetric accuracy of conventional digital cameras, which was evaluated based on the CIEDE2000 metrics and the creation of camera ICC profiles, as well as the calculated profile volumes. By comparing the average CIEDE2000 color differences between the cameras and profile volumes, we observed a trend indicating that cameras with larger profile volumes (color gamut) provide lower CIEDE2000 color difference values, and vice versa. Based on the results and comparison between the capture using 3- and 6-channel devices, it can be concluded that the use of a 6-channel camera resulted in a highly accurate (in terms of colorimetry) multi-channel capture, as indicated by the average CIEDE2000 differences, which showed a significant improvement in favor of the 6-channel capture

3D Digital Preservation, Presentation, and Interpretation of Wooden Cultural Heritage on the Example of Sculptures of the FormaViva Kostanjevica Na Krki Collection

The paper presents an interdisciplinary approach to the treatment of the FormaViva collection of wooden sculptures exhibited outdoors in a natural environment near the Božidar Jakac Art Museum in Kostanjevica na Krki in Slovenia. The study focuses on 3D graphic representations of sculptures created with photogrammetry and 3D modelling. The results are photorealistic renderings, interactive presentations, 3D printed reproductions, jewellery, and interpretive animations. The research results show that graphic documentation techniques on 3D models allow for a more detailed investigation of the original structural identity of the sculpture. By incorporating 3D and interactive technologies, we are expanding the usability of cultural heritage objects. By using interpretive techniques that have led to jewellery and interpretive animations in our research, we not only breathe new life into the sculptures, but also enrich the stories of the sculptures with our own experiences of the sculptural work